Responses of potassium-depolarized rat tail arteries to adrenaline and serotonin.

Dose-response curves to adrenaline and serotonin were obtained from tail arteries incubated in standard, high potassium or low sodium media. The last one was used to test whether the effects of high potassium medium could be influenced by the concomitant lowering of the sodium concentration. The effects of endogenous catecholamines were eliminated by means of reserpine pretreatment, in vitro denervation with 6-OHDA or adrenergic blockade with phentolamine. Any of these procedures abolished the sustained contractile responses to high potassium, which then produced only small transient contractions. Dose-response curves to serotonin were not altered in the high potassium medium whereas those to adrenaline displayed slight changes. Inasmuch the responsiveness remained almost unchanged even though the effects of either agonist on the membrane potential had been virtually abolished, it was concluded that pharmacomechanical coupling is the major mechanism involved in the contractile responses of the tail artery.